Because if a product uses a 32 bit counter to record uptime, and that counter records a tick every 10 msec, then that 32-bit counter will overflow after approximately 497.1 days. This is because a 32 bit counter equates to 2^32, which equals 4,294,967,296 ticks. If a tick is counted every 10 msec, we create 8,640,000 ticks per day (100*60*60*24). So after 497.102696 days, the counter will overflow. What happens next depends on good programming: normally the counter just starts again, but worst case a function might stop working or the product might even reboot.

Fortunately we are seeing less and less of these issues but just occasionally one still slips out. Recently IBM released details of a 994 day reboot bug in the ESM code of some of their older disk enclosures (EXP100, EXP700 and EXP710). Details about this bug can be found here. What I find interesting is the number of days it takes to occur, since 994 is actually 497 times two. This suggests that this product records a tick every 20 msec. This meant we got past 497 days without an issue but hit a problem after exactly double that number. So if you still have these older storage enclosures, you will need to reboot the ESMs (after checking the alert).

I googled 497 to see what images that number brings up and was amazed to find the M-497 jet powered train. More details on this rather interesting attempt at speeding up the commute home can be found here and here. It adds a whole new meaning to keeping behind the yellow line.

I always laugh when people say to me: I wouldn't know what to blog about!

When you work in pre-sales support, you constantly get asked questions and each one of them could be the subject of a new blog post. Right now the most common question I am getting is:

I am implementing VMware Site Recovery Manager (SRM). One of the components I need are vendor specific Site Recovery Agents (SRA). I have searched IBM's website but cannot find them. Where are they?

So the short answer is: you get them from the VMware SRM download site.However before downloading, there is a key task that absolutely needs to be performed:

Visit the VMware vCenter Site Recovery Manager Storage Partner Compatibility Matrix. This site will confirm what products are supported by each version of SRM. You can find it here, but clearly you need to check back regularly to ensure you have the latest information.

Now find your storage device in the matrix and confirm what firmware levels are supported. This is really important. For example, the Feb 27, 2012 edition of the matrix tells me that the Storwize V7000 is supported for SRM version 5.0, but only when running Storwize V7000 firmware version 6.1 or 6.2. This is significant because if you upgrade to version 6.3 you are not supported. In fact that combination doesn't actually work yet, as detailed here. Clearly something you need to be aware of when planning firmware updates.

So where are the SRAs? On each of the pages below use the Show Details button to see what version SRAs are being shipped with that SRM (although sometimes the pages take a few days between an SRA being added and the page being updated):

The answer is yes, but it is an FTP site only for SRAs written by IBM. It is principally a repository for older SRAs and beta SRAs but you can also find the current SRAs on it. You can find the site here. Note however that it is NOT the official source. For that you need to use the VMware site.

What about the SRA for LSI/Engenio based products like the DS4800?

These used to also be found on the LSI site, but since LSI sold Engenio to NetApp, it is no longer available from the LSI or NetApp websites. You need to download the current version from the VMware sites listed above. There is a version for SRM 5 on the VMware download site.

What about nSeries SRAs?

If you need an nSeries SRA, again you should go to the VMware download pages. There are separate SRAs listed and available for IBM nSeries (as opposed to an SRA for NetApp branded filers).

What about an SRA for XIV with SRM version 5?

The answer: The SRA for XIV with SRM 5 (and 5.0.1) is now available from VMware. If you have access to download SRM, you will be able to download SRA version 2.1.0. It is the same SRA for both XIV Generation2 and Gen3.

What about an SRA for Storwize V7000 and SVC version 6.3 code?

The answer: It is coming. We are working to make it available as soon as possible. I will update this post as soon as I have a date for you (we are talking weeks, not months).